As is known, power distribution networks are used for delivery to end users of electricity produced at power stations and made available through high-voltage transmission networks. Distribution networks, generally operating in the medium voltage range (between 1 kV and 30-75 kV for alternating current and between 1.5 kV and 30-75 kV for direct current, according to the definitions given in a number of national standards), comprise, besides, of course, the medium voltage lines, primary substations, secondary substations, and one or more supervision and control apparatuses. The primary substations convert the voltage from high to medium and supply power to the secondary substations, which convert the voltage from medium to low and deliver it to the end users.
An ineliminable function to be implemented by respective switchboards from both primary and secondary substations concerns the protection of the network, i.e. the detection and signalling of faults (overloads, short circuits, electric arcs between phases, interruptions, and so forth) and the ability to implement emergency manoeuvres such as opening the switches and insulating network sections in which the faults detected are located. The signalling of faults, obviously, cannot leave aside communication to surrounding switchboards and to the supervision and control apparatus. For this purpose, Ethernet line and fibre-optic connections, or wireless connections, are used. In addition, communications can be based on specific protocols.
Given the critical nature of the protective functions, the connections are usually redundant. Nevertheless, accidents may occur which make the connections simultaneously unserviceable for more or less extended periods of time. In some cases, the connection malfunctions can be resolved quickly through actions requested by self-diagnosis or remote functions, such as restore operations (reset) of the equipment concerned. Other times, the damage may be more severe with longer downtime. For example, some of the equipment may fail or the lines can may severed during the execution of works, thus requiring replacement. In all such cases, however, the protective functions of a part of the medium-voltage network are impaired for a period of time.
Therefore, there is a need to strengthen the communication of the primary and secondary substation switchboards of the medium-voltage networks with each other and with the supervision and control apparatus, reducing the risk of disruption of the protective functions. At the same time, it should be borne in mind that it is appropriate not to weigh too heavily on the costs of construction, management and maintenance of the networks.